Richard Aerni on mon 10 dec 07
Hello everyone,
Recently the issue of barium use and barium safety has come up again on the
list, and people have weighed in with their opinions and beliefs. However,
none of this discussion has actually referenced published data with author's=
accountability. It has mostly just been putting forth one's opinions, based=
on either experience or research, without quoting any facts or figures.
With that in mind, I looked up an old article in Ceramics Monthly (September=
1997) by Jeff Zamek, a potter and ceramics consultant located in
Massachusetts. He has written it from the standpoint that knowledge allows
for informed decision-making, and has shared his knowledge and research in a=
way that I haven't seen in other articles or discussions. I talked with him=
today to see if it would be OK to add it, in it's entirety, to clayart, and
thus enter the archives for use as a research aid in future discussions on
the subject. He said it would be fine to do so. I also asked him if he had=
come across any further studies since the article was published that would
cause him to change any of his thoughts on barium carbonate. He said he had=
not.
So, without further ado, I include his article below. A caveat...I have no
horse in this discussion...I mostly wish to see informed discussion continue=
and flourish. Also, any typos or omissions are mine, due to my keyboarding
skills, and not Jeff's or CM's.
Best,
Richard Aerni
Rochester, NY
Is Barium Carbonate Safe?
By Jeff Zamek
From September 1997 Ceramics Monthly
Yes=97provided you don=92t go into your studio and eat or directly inhale ba=
rium
carbonate. That is the short answer to a controversial issue raised by many=
in the field of ceramics. However, knowledge of the material, especially in=
the raw form, is vital to a potter=92s health and safety.
Barium carbonate has a long history of use in clay bodies, casting slips and=
glazes in which it serves several functions. Regardless of this history,
today many potters are removing barium from their studios, fearing its toxic=
potential.
As the general population has become more aware of health and safety issues,=
every material is being examined for its potential harmful effects.
Understandably, potters do not want to jeopardize their health when handling=
raw materials, nor do they want to place their customers at risk when using
their fired clay and glaze products. With such legitimate health and safety=
concerns, why use barium carbonate?
In clay bodies
We have all noticed surface deposits of white powder developing on exposed
parts of common red building brick. The soluble salts in the clay migrate
to the brick surface, causing white scumming. When barium carbonate is
added to the clay body (0.25% to 2% based on the dry weight of the clay
body), it reacts with the calcium and/or magnesium salts in the clays,
changing them into calcium carbonate and barium sulfate, which do not
produce soluble salt scumming. By eliminating soluble salts in the clay
body, subsequent firing discoloration is reduced. Some red earthenware
clays are more susceptible to soluble salt problems, but even so-called
=93clean=94 clays can occasionally have high levels of troublesome salts.
Consequently, the use of barium carbonate is advantageous in many different
types of clay bodies.
In casting slips
Ball clays used in casting slips sometimes contain soluble salts. If the
ball clay was left untreated, it would require excessively high amounts of
deflocculant to transform it into a casting slip. Barium carbonate reacts
with soluble salts found in clays, changing them into insoluble barium
sulfates, which in turn reduces the deflocculant requirement for the slip.
In low-fire white clay bodies, where the amount of ball clay can be as much
as half the clay body recipe, the level of barium carbonate required can be
0.03% to 0.05%, based on the dry weight. The actual amount required will
depend on the soluble salt levels found in the clay.
In stoneware and high-iron-content casting slips, barium carbonate is needed=
to facilitate good casting properties and can be as high as 2%, again based
on the dry weight of the recipe.
In glazes
Barium carbonate can be classified as an alkaline earth that is very
refractory. Its use promotes unique glaze colors and surface qualities that=
are very difficult to obtain when using alternative glaze materials. Small
percentages in low-temperature glazes will result in dry matt surfaces. At
higher temperatures, barium carbonate is mostly known for producing soft,
buttery glaze textures. It can also yield intense blue colors when combined=
with copper in reduction glazes.
Alternatives
Sometimes, if less than 6% is used in high-temperature (above cone 6 or 2194=
degrees Fahrenheit) glaze recipes, and it is not needed to promote color or
glaze texture, barium carbonate can be removed without changing the fired
nature of the glaze. In such situations, barium is acting as a marginal
flux. Its absence will not appreciably affect the fired glaze result. In
glazes containing amounts greater than 6%, the barium carbonate is probably
contributing to opacity and glaze color, and removing it would substantially=
change the glaze.
Strontium, which goes into a melt more actively than barium, has been used
as a substitute (3/4 part strontium carbonate to 1 part barium carbonate),
but it does not yield an adequate match in glaze color, opacity and texture.=
Barium sulfate (the insoluble and nontoxic form of barium used to medical
procedures) is another ineffective barium carbonate substitute in glazes or
clay bodies. Sulfate fumes are released as the barium reacts with
increasing kiln temperature, causing blisters or pinholes in glazes and
bloating in clay bodies.
Facts about barium carbonate
The barium carbonate material that potters use in clays and glazes is never
found in nature in its elemental form, bit is mined from barite ore that
contains barium sulfate. Barite is a naturally occurring mineral used in
the oil and gas-drilling industries. About 5% of barite is processed into
barium carbonate, barium chloride and barium hydroxide. Barium carbonate is=
used in the manufacture of glass for television and computer screens due to
its capacity to absorb X-rays generated when the image is produced. Barium
carbonate is also blended with iron oxide to form ceramic magnets used in
many products. Various industries in the United States use approximately
50,000 tons of barium carbonate every year. See =93Toxicology and
Carcinogenesis Studies of Barium Chloride Dihydrate (Drinking Water
Studies), =93 U.S. Department of Health and Human Services, case number
10326-27-9, pages 13-16.
A search of the relevant medical literature and journals reveals two kinds
of problems associated with toxic reactions to raw barium carbonate. Barium=
carbonate can be accidentally ingested/inhaled, or it can be intentionally
ingested to commit suicide.
Toxic effects of ingestion
The effects of ingestion take place when barium carbonate changes in the
presence of stomach acid (hydrochloric acid), yielding soluble barium
chloride. The first symptoms can be vomiting, skeletal and muscle twitching=
or muscle paralysis. If ingested, small amounts of barium carbonate (13
grams) can be lethal. One woman attempted suicide by eating 40 grams of
barium carbonate. She required mechanical ventilation after her respiratory=
muscles were paralyzed, but recovered fully within one week, according to D.=
M. Phelan, S. R. Hagley and M. D. Huerin in =93Is Hypokalemia the Cause of
Paralysis in Barium Poisoning?=94 British Medical Journal, volume 289, page =
882.
Another example of intentional ingestion of barium involved a man who went
on a drinking spree, bingeing on ethanol for one week, then ingesting about
13 grams barium chloride in an attempt to commit suicide. He developed
paralysis involving the extremities, his respiration became paralyzed and he=
was placed on mechanical ventilation. Magnesium sulfate was administered,
and the patient made a rapid recovery after an 11-day hospital stay. This
case was documented by S. F. Wetherill, M. J. Guarino and R. W. Cox in =93Is=
Acute Renal Failure Associated with Barium Chloride Poisoning?=94, in Annals=
of Internal Medicine, volume 95, number 2, pages 187-188. Such cases are
significant in that barium ingestion was by intent, not by accident.
A case of unintentional ingestion was documented when seven people in one
family accidentally consumed rodenticide (barium carbonate) and required
treatment at their local hospital; reported in the Annals of Emergency
Medicine by C. H. Johnson and V. J. Van Tassell in October 1991, pages 1138-=
42.
Most barium that enters the body is eliminated within one or two weeks.
See the =93Toxicological Profile for Barium=94 issued by the U. S. Departmen=
t of
Health and Human Services, Public Health Service, Agency for Toxic
Substances and Disease Registry, PB 93-110658.
Barium is not a cumulative substance in the body where at some point a
toxic level could be reached. Past information about barium causing
cumulative central nervous system damage is not supported by the
Environmental Protection Agency=92s toxicological evaluation of soluble bari=
um
in the Federal Register, volume 62, number 2, January 3, 1997, pages
368-370. However, just on a commonsense level, it would still be a prudent
step to store barium carbonate in a clearly labeled covered jar. Accidents
do happen in every area of life.
Toxic effects of inhalation
Breathing in particles of any substance found in the pottery studio should
be prevented. Whenever clay and glaze materials are handled in the dry
state, small particles often become airborne. Wearing a dust mask in
situations where bags of dry materials are opened or mixed is a safeguard
against inhalation of these particles.
In the medical literature, one case demonstrates what types of problems
potters are not having with barium carbonate. A 22 year-old man (who was
new on the job) caused an explosive blowback into his face by dumping barium=
into another material. He was not wearing a dust mask and inhaled a
considerable amount of powder, but did not swallow much. He experienced
cramps and nausea; his feet and hands felt heavy and weak. At the hospital,=
he was treated with potassium intravenously and completely recovered in five=
days. This case was studied by R. Shankle and J. R. Keane, =93Acute Paralys=
is
from Inhaled Barium Carbonate,=94 Archives of Neurology, volume 45, pages 57=
9-580.
While such cases are sensational and thought provoking, they do not reflect=
potters=92 experiences with barium carbonate. Studio potters are not likely=
to encounter a case where barium carbonate is involved in an explosive
reaction, but this accident does illustrate the need for a dust mask.
No reported potter=92s reactions
For more than 40 years, potters in the United States have been using barium=
carbonate in their studios and have sold functional pottery with
barium-containing glazes. The medical records do not show any reports of
toxic reactions to barium carbonate used in pottery studios or toxic levels
of barium released from glazes. Databases searched include BIOSIS
(toxicological aspects of environmental health), TOXLIT (toxicology
literature), RTECS (Registry of Toxic Effects of Chemical Substances), and
MEDLINE. This lack of documentation indicates two possibilities: potters
are receiving toxic doses of barium carbonate in their studios and their
symptoms (vomiting, paralysis, etc) are not recognized or reported; or toxic=
reactions to barium carbonate simply are not happening.
In fact, an occupational exposure study reported no adverse health effects
related to workers exposed to high levels of barium carbonate dust for
periods of 7 7o 27 years; see =93Exclusion of Disturbances to Health from Lo=
ng
Years of Exposure to Barium Carbonate in the Production of Steatite
Ceramics: by H. G. Essing, et al. in Arbeitsmedizin Sozialmedizin
Praventimedizin, volume 11, number 12, pages 299-302.
Clearly the published warnings about barium carbonate usage should be taken=
seriously; however, precautionary measures should remove the potter from any=
short- or long-term hazard due to inhalation and ingestion.
Safe Handling in the Studio
Essentially, the same safety precautions should be in effect when handling
any raw material. Whenever possible, purchase materials in clean, unopened
bags and store them in covered containers or large heavyweight plastic bags
with twist-top closures. During clay- or glaze-mixing operations,
immediately return any unused raw material to the covered jar or storage
bag. In this way, bags will not accidentally be broken open, causing small
particles of raw material to spread throughout the studio. When opening a
raw-material bag or mixing dry materials, always wear a dust mask,
preferably a cartridge respirator in which the filter is changed regularly.
Barium carbonate has limited solubility in pure water. Solubility of
barium carbonate in glaze water varies with pH levels, but remains marginal.=
If the glaze water is acidic (low pH levels), some barium carbonate changes=
to barium chloride, with levels in the water of 15.3 ppm to 45 ppm. Such
amounts are well below any toxic concern for absorption through the skin,
even with an open wound on the hand.
While mixing a wet or dry glaze with your hands is not recommended, the
medical literature does not contain any reports of barium carbonate
migrating through wounds in the skin. By way of comparing the relative
risks in glazing operations, mixing high-alkaline and soluble wood ash
glazes with bare hands is more harmful, as this will cause skin irritation
and/or burns. Regardless, washing hands after any glazing operation is
always best.
Barium in the environment
Barium in its different forms, is commonly found in food, water, soil and
even the air we breathe. It is one of the most abundant materials found in
the earth. We are in a barium-laden environment. The =93Toxicology and
Carcinogenesis Studies=94 report issued by the U. S. Department of Health an=
d
Human Services states that the drinking water in some United States cities
can exceed 20 ppm. This amount reflects what people are consuming daily
without ill effects; it does not tell us what amount greater than 20 ppm
people could consume with no ill effects.
In the past, long-term exposure to low levels of barium were thought to
cause health problems, but the data do not support this belief. The
National Toxicology Program Study by the U. S. Department of Health and
Human Services conducted tests in which animals were given water containing
up to 700 ppm barium. At this level of daily consumption, the water did not=
produce harmful effects and was considered safe to drink. The medical
assumption in this method of testing is that animals respond similarly to
humans.
Humans ingest barium on a regular daily basis. It is found in many foods,
including tea, coffee and fruits. Dietary consumption of barium from foods
is from 300 to 1770 mg/day. Barium is also found in bran flakes (3.9 ppm),=
eggs (7.6 ppm), sea water (5.2 ppm), beets (2.6 ppm), and Brazil nuts (1000
ppm), but even at that amount, the chances of anyone eating enough Brazil
nuts to achieve a toxic level of barium are remote, as the stomach and
digestive system could not hold that bulk.
Barium release from glazes
Barium carbonate decomposes when heated, and changes to barium silicate or
barium salts in the fired glaze, after which the glazed surface can release
barium when in contact with weak acids contained in foods. Release levels
of fired glazes containing barium can range from 0 ppm to more than 1250
ppm; however, many glazes tested are within the 20 ppm barium-release ranges=
.
It is always prudent and useful to test for barium-release levels on
functional pottery glazes that come into direct contact with food or drink.
If the test is done correctly, the accuracy rate is 99%. Choose a
laboratory that is familiar with the testing procedure. For example, a test=
for barium release or other elements in glazes (ie, antimony, manganese,
vanadium, lead, etc.) can be done by sending a fired sample of the glaze on
a cup or bowl to Office of Sponsored Programs, New York State College of
Ceramics, Alfred University, Alfred, NY 14803; there is a $30 charge per
element tested.
Commonly high-barium-release levels in glazes can be substantially
decreased by firing the glaze one or two cones higher or by adjusting the
glaze constituents. If you are unsure of how to adjust the glaze, seek
guidance. Experimenting on your own without a basic understanding of glaze
materials can be fun, but it can also be time consuming. Often, the most
efficient method is to obtain several barium glaze recipes that have already=
been tested.
Summary
As potters, we should educate ourselves about the safe use of any raw
material in our studio. We should then use this knowledge to protect
ourselves and our customers from any potentially harmful effects. However,
we are often asked to make decisions about ceramic materials based on
incomplete facts. In the past, unchallenged claims, unfounded dire
projections, and generalizations about raw-material hazards were more drama
than documented fact. In some circumstances, the information published has
not been relevant to how we as potters use the material. An ongoing effort
to increase our knowledge of questionable materials will yield a realistic
evaluation of potential hazards.
Often a valid disagreement exists on which materials are truly dangerous.
Such differing opinions are beneficial, as they contribute to discussions,
testing, and greater research in ceramic raw material toxicology as it
directly relates to potters.
The health and safety issues concerning potters=92 use of barium carbonate
fall into two primary areas of concern: The accidental ingestion/inhalation=
of the material in the studio, and its potential release from fired glazes.
To prevent accidental inhalation/ingestion, store in covered containers and=
wear a dust mask when mixing or handling barium carbonate. Sometimes a
simple recommendation is not considered valuable or effective because it is
too easy to believe.
The second area of concern relates to the potential release of barium used
in clay bodies, casting slips and glazes. The low percentages of barium
carbonate used in clay bodies and casting slip recipes, and its low
potential for release negate any level of concern regarding health and safet=
y.
In glazes, the ideal is an inert, stable, non-leaching fired surface, but
this situation is not necessary for barium=97although it should be for lead
and other heavy metals, which are highly toxic and can accumulate in the
body. With the level of barium release in some communities=92 drinking wate=
r
approaching 20 ppm with no ill effects on the population, a 20 ppm or lower
release of barium for functional pottery glazes should be a conservative
goal. This amount takes into consideration various factors that can cause
variable barium-release levels in glazes, such as glaze thickness, firing
atmosphere, endpoint firing temperature, time to temperature, refiring
glazes and marginal glaze testing inaccuracies.
The drinking water study (=93Toxicology and Carcinogenesis Studies of Bariu=
m
Chloride Dihydrate=94) is significant because it relates to a
barium-consumption level in water (20 ppm) over a prolonged time. This is
the closest approximation to people drinking or eating from barium-release
glazes for an extended time. It also assumes the worst case situation where=
a glaze releasing barium will continue to release the same amount of barium
every time it contacts food or drink.
Barium carbonate is not an easy material to classify concerning safety
issues. It requires respect and effort to understand how to use it safely.
Potters can always take the recommendations of =93experts,=94 but real
knowledge comes from building up a base of information from many sources.
Disregarding raw-material warnings is irrational, just as believing the
=93poison of the month=94 theory is excessive. Both extremes are inaccurate=
and
foster ignorance instead of insight.
Potters must do some hard work and look into the literature and toxicity
statistics on this common glaze material. On some level, we calculate the
relative risk factor in all daily events. How dangerous is flying? Not as
dangerous as driving to the airport.
How dangerous is barium carbonate as used by potters? Not as risky as back=
pain from lifting kiln shelves, nerve damage from carpal tunnel syndrome
(repetitive motion injury from throwing, wedging, lifting) or retina damage
from looking into a firing kiln without eye protection. Proper protection
and knowledge will prevent accidents in these know potential areas of risk.
The same principle should be applied to barium carbonate.
The author A frequent contributor to CM, ceramics consultant Jeff Zamek
resides in Southampton, Massachusetts; he recommends potters attend an
online discussion concerning =93Toxic Materials in Ceramics=94 on America
Online=92s Hands in Clay chat room September 18, 1997 at 9 pm EDT.
Richard Aerni on tue 11 dec 07
I neglected to mention in my original post that Jeff covers this same
subject in chapter 21 of his book, "What Every Potter Should Know."
Best,
Richard Aerni
Rochester, NY
Ivor and Olive Lewis on tue 11 dec 07
Dear Richard Aerni,
Thank you for reproducing J. Z's Article. But I think more information =
is needed. It seems to me that some of the essential knowledge about =
substances that contain the element Barium is being ignored. =
Furthermore, the chemical behaviour of Barium Carbonate and Barium Oxide =
towards other ingredients seems to be unexplored.
The CRC Handbook lists two silicates, a Metasilicate which has a melting =
point of 1605=BA C, is insoluble in water but soluble in acids and a =
Disilicate with a MP of 1420=BA with no other information. Leaning =
towards caution, it would seem advisable to assume that even if glaze =
recipes that contain small fractions of Barium are transparent and =
glossy, they will be subject to degradation and dissolution in even the =
mildest acid (Water saturated with carbon dioxide).
Regarding Barium Carbonate, I have the impression that there is an =
assumption circulating that this substance will behave as does Calcium =
Carbonate, that it decomposes when heated. This is partly true. But =
Earnshaw and Greenwood qualify this with a reaction temperature of 1350 =
deg C, much higher than the decomposition of CaCO3. Perhaps up to Cone =
11 this material does not decompose. If it remains unaltered in the =
glaze then it will be exposed and open to attack by acidic solutions.
So far, as I recall, no one has thought about Barium Oxide. If, in a =
glaze, Barium carbonate does decompose, there may be residual unaffected =
Barium oxide exposed at the surface. This would be slightly soluble in =
Water as well as soluble in acid. Frank Hamer tells us that BaO is =
reactive towards water but has our attention been directed to this ?
Perhaps it is time to reassess and update some of our knowledge.
Best regards,
Ivor Lewis.
Redhill,
South Australia.
Richard Aerni on tue 11 dec 07
On Tue, 11 Dec 2007 17:19:59 +1030, Ivor and Olive Lewis
wrote:
>Dear Richard Aerni,
>
>Thank you for reproducing J. Z's Article. But I think more information is
needed. It seems to me that some of the essential knowledge about substances
that contain the element Barium is being ignored. Furthermore, the chemical
behaviour of Barium Carbonate and Barium Oxide towards other ingredients
seems to be unexplored.
Ivor,
I couldn't agree more! Definitely more research and more information is
needed. That is why I threw out Jeff Zamek's article. I certainly don't
need to tell you that nothing is ever "proven" in science...a theory is
relevant and operative as long as current research says so, or until
something new comes along that either further refines or disproves.
I guess I would say, as has Jeff Zamek and others, that one should educate
oneself, use materials carefully, and keep up with the current literature.
But to make a blanket statement that it is OK to use barium, or absolutely a
problem is to oversimplify and cut off discussion and research.
Once again, I don't have a side in this. I'm just wishing for enlightened
inquiry and discussion.
Best,
Richard Aerni
Rochester,NY
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